Everyone remembered Kafka's eyes. Large, luminous, intense. Yet no one, not even his lovers, could agree on their colour. Some testified to their being steel blue, others grey, while still others insisted they were brown. The skill in Nicholas Murray's gripping biography lies in allowing even the most glaring inconsistencies of life to remain unresolved, in letting every aspect of Kafka's complex vision glisten across the decades since his death in 1924.

'Kafkaesque', one of the most expressive 20th-century buzzwords, owes much of its peculiar power to the fuzziness of its definition. Any biographer of Franz Kafka must likewise face the challenge of pinning down his mysterious essence.

Part of the problem is Prague itself. The teetering social structures into which Kafka was born in 1883, a German-speaking Jew among Czechs, were unlikely to foster much inner stability or confidence. Add to this the unforgiving expectations that Kafka's father, Hermann, would place on his son and one begins to glimpse the crushing emotional, cultural, and religious environment in which Kafka was raised.

Though a maker of walking sticks by trade, Hermann's disdainful manner would have a crippling effect on Kafka's fragile psyche. Many of his son's habits, including his vegetarianism and rejection of alcohol, let alone serious neuroses - hypochondria, paranoia, and periods of intense self-loathing - are often pinned on Hermann's overbearing nature. But Murray is cautious of flimsy caricatures, and laudably emphasises moments of remembered tenderness as well.

Still, there is little denying Kafka's propensity for despair. Indeed, he would become one of literature's great self-sabotagers of talent. His ability to undermine his own artistic promise by sinking enormous chunks of energy and affection, not to mention time, into masochistically chasing the wrong woman characterises much of his sad story.

A lawyer for an insurance company by day, Kafka's evenings represented precious opportunities for him to write, the one activity that he believed justified his existence. Yet crucial months of his creative development were wearied away by insomniac scribbling of endless letters (sometimes more than 50 a month) to Felice Bauer, a woman from Berlin he had met only once, and towards whom he knew deep down he was romantically ambivalent at best.

Though Bauer showed no sign of appreciating, let alone encouraging, Kafka's genius, he clung to her like a drowning man to a punctured buoy, haranguing her with more than a quarter of a million words of desperate correspondence over the course of five years and two abortive marriage proposals.

Kafka's tendency towards fragmentation in both his personal and creative lives makes for excruciating reading. The burned-out husks of abandoned relationships and half-finished writing projects litter the landscape of his universe.

Given Kafka's difficulty in cultivating connections with women, there is little wonder that he soon became obsessed with the idea of suicide as a form of brutal self-consummation. And it is in this brittle frame of mind that his memorable alter-ego, Joseph K, makes his first public appearance in the short story A Dream.

The setting for the vision is a cemetery where Joseph K meets an artist lettering a tombstone in gold. Slowly, Joseph K comes to realise that the grave is for him and proceeds to climb dutifully into it.

A tragic countermovement to Kafka's growth as an artist is the relentless deterioration of his young body. A subplot of fevers and stomach pumpings builds to its heartbreaking climax in the diagnosis of tuberculosis when he was in his late 30s. With characteristic gloominess, he accepts the hopeless prognosis as some sort of cosmic punishment for unspecified sins of the soul.

Kafka died at 40 and, in his will, instructed his lifelong friend Max Brod to destroy his unpublished writings, believing them unworthy of posterity. It seems somehow fitting that Kafka, with whom we most closely associate the fear of arbitrary legal decisions, should for eternity owe his reputation to Brod's wilful refusal.

Though passionately engaged, Murray avoids hero-worship, offering equal space to doubters such as Edmund Wilson, who insisted Kafka's works were little more than 'the half-expressed gasp of a self-doubting soul trampled under'. The result is a soulful, searching book, faultlessly researched and beautifully written.